Penicillin can be used for three days to see the effect, if it is an infectious disease, three days time the condition does not get better indicates that it is not sensitive to penicillin, if it is not an infectious disease should not use antibiotics to treat. Penicillin is a kind of antibiotic, generally need to use continuously for about three days to assess the therapeutic effect, if the condition improves, then it shows that penicillin is effective for the patient can continue to use, the general consolidation of the course of treatment for 1~2 weeks, penicillin can not be used for too long, so as not to produce side effects as well as drug resistance. If you use penicillin for three days or so, there is no improvement in your condition, which means that your condition is not sensitive to penicillin, and you need to change to other antibiotics under the guidance of your doctor. It is important to note that before using penicillin, you must ask the patient’s allergy history and do a skin test to avoid allergic reactions.